Infrared microscopes are typically used in conjunction with an IR spectrometer to analyze small samples of various materials.
An infrared microscope typically receives infrared radiation from a source in the spectrometer. The microscope will include a sample stage for carrying a sample to be analysed and a series of optical elements for guiding radiation from the radiation source to the sample stage. These optical elements may include mirrors, lenses, and condensers. The infrared radiation is directed to an infrared detector, typically via a magnification assembly. The sample may also be viewed optically by means of visible radiation, i.e. the microscope functions in both the visible and the infrared spectrums. A variable aperture, which may be computer controlled, is located at the intermediate image plane. The variable aperture enables portions of the sample to be masked.
There is a need to be able to vary the magnification. Known IR microscopes achieve variable magnification via external interchange of the objectives. Others enable the exchange of internal focal plane array (FPA) optical elements, for example, by placing additional lenses or mirrors in the optical path. However, such systems have a number of disadvantages including limited wavelength coverage of the FPA optical elements where lenses are used, and a relatively difficult task of aligning the FPA optical elements due to the multiple surfaces of the lens system. The hygroscopic nature of lenses may lead to degradation in resolution and lenses may further be subject to chromatic aberrations. Moreover, approaches that rely on changes to typical FPA optical element configurations must be incorporated into each microscope at the time of manufacture. That is, it is not generally possible to add the capability to vary magnification to known microscopes that were not built with that capability.
What is needed, therefore, is an infrared microscope that overcomes at least the shortcomings of the known microscopes described above.